Six fertilizer samples with different NPK ratings (4–13% N; 4–15%
P
2
O
5
;6–18% K
O) were purchased at a local market in Araraquara city
(São Paulo, Brazil). The samples were reduced in size by coning and
quartering: around 1 kg of sample was poured out to form a conical
heap, which was then spread out into a circular disk of material with a
spatula. The disk was divided radially into quarters, two quarters were
discarded, and the remaining two quarters were combined. The process
was repeated until a sample mass of approximately 5 g was obtained.
The samples were prepared in triplicate according to the procedures
laid down by the Brazilian Ministry of Agriculture, Livestock, and Food
Supply (MAPA) and the official AOAC International method of analysis.
Both procedures were employed for analysis of the fertilizers by the
proposed HR-CS FAAS method and by the comparative techniques, as
described below: